Method for producing an no electric strip of intermediate thickness

ABSTRACT

The present invention relates to a process for producing a non-oriented electrical steel strip, comprising at least the following process steps (A) provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip, (B) cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip, (C) intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip, (D) cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip and (E) final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip, a non-oriented electrical steel strip obtained in such a way and the use thereof.

TECHNICAL FIELD

The present invention relates to a non-oriented electrical steel strip having a specific composition and texture, a process for the production thereof, comprising at least the following process steps (A) provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip, preferably by the conventional manufacturing route via a continuous casting plant or by thin slab manufacture, in a thickness of from 1 to 4 mm, (B) cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip, (C) intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip, (D) cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip and (E) final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip.

TECHNICAL BACKGROUND

Non-oriented (NO) electrical steel strip is used for increasing the magnetic flux in iron cores of rotating electric machines, i.e. in motors and generators. Future highly efficient electric machines, e.g. electric motors having high speeds of rotation for traction drives of electric vehicles, will require specific types of NO electrical steel strip having a low magnetic loss at high frequencies and high magnetic polarization or induction with high permeability.

Components manufactured from electrical steel strips or sheets of the type in question here require the abovementioned magnetic properties which often cannot be satisfied by the types of NO electrical steel strip available today. Non-oriented electrical steel strips and two-stage processes for the production thereof are already known from the prior art.

Thus, WO 2015/170271 A1 describes, for example, an NO electrical steel strip or sheet which has a low loss as a function of the thickness and is made of a steel which contains, apart from iron and unavoidable impurities, (in % by weight), from 0.001 to 0.01% of C, from 1.8 to 6.0% of Si, from 0.2 to 4.0% of Al, from 0.2 to 3.0% of Mn, from 0.0005 to 0.01% of S, from 0.001 to 0.01% of N and in which the ratio of Mn content to S content is more than 100 and the ratio of Al content to N content is more than 200. The steel having such a composition is cast to give slabs having a thickness of greater than or equal to 20 mm, which are optionally reheated in the range from 1000 to 1330° C. and subsequently hot rolled in the range from 1300 to 700° C. to give a hot-rolled strip having a degree of deformation of from 70 to 99% in order to obtain a hot-rolled strip thickness of from 2.5 to 12 mm. The hot-rolled strip is cold rolled with a total degree of deformation of at least 80%. A first cold rolling step is carried out with a degree of deformation of from 20 to 70% at a temperature below 300° C. The cold-rolled strip is subjected to an intermediate heat treatment at from 700 to 1100° C. for a time of from 10 to 900 s. This is followed by a second cold rolling step with a degree of deformation in the range from 20 to 70% to a final thickness of from 0.15 to 0.5 mm. The second cold rolling step can be repeated a third time with additional heat treatment. The cold-rolled strip obtained is subsequently subjected to a recrystallization heat treatment in which it is heat treated at a temperature of at least 800° C., but at a heat treatment temperature of less than 1200° C., for a time of from 10 to 900 s.

In the light of the prior art indicated above, it was an object of the invention to provide an NO electrical steel strip or sheet and a component manufactured from such a sheet or strip for electrotechnical applications, which displays low magnetic losses and at the same time high polarization values, achieved by means of an improved texture. These low magnetic losses should be achieved under standardized conditions at 1.5 T and 50 Hz and high polarization values J2500 and J5000, but low magnetic losses should also be achieved at higher basic frequencies of, for example, 400 Hz, 700 Hz, 1000 Hz or more. These low magnetic losses and high polarizations should be displayed by, in particular, non-oriented electrical steel strips having a silicon content of from 2.1 to 3.4% by weight of Si.

In addition, a process for producing such an NO electrical steel strip or sheet which has good processability, in particular at low final thicknesses, should be indicated.

These objects are achieved by the non-oriented electrical steel strip according to the invention and by the process for the production thereof, comprising at least the following process steps:

-   -   (A) provision of a hot-rolled, optionally separately         heat-treated, non-oriented electrical steel strip, preferably by         the conventional manufacturing route via a continuous casting         plant or by thin slab manufacture, in a thickness of from 1 to 4         mm,     -   (B) cold rolling of the electrical steel strip from step (A) to         a thickness of from 0.5 to 0.8 mm in order to obtain a first         cold-rolled strip,     -   (C) intermediate heat treatment of the first cold-rolled strip         from step (B) at a temperature of from 700 to 1100° C. in order         to obtain an intermediate-heat-treated, first cold-rolled strip,     -   (D) cold rolling of the intermediate-heat-treated, first         cold-rolled strip from step (C) to a thickness of from 0.24 to         0.36 mm in order to obtain a second cold-rolled strip and     -   (E) final heat treatment of the second cold-rolled strip from         step (D) at a temperature of from 900 to 1100° C. in order to         obtain the non-oriented electrical steel strip.

In order to reduce the magnetic losses of machines and to increase the polarization, very thin electrical steel strips or sheets having an optimal texture are sought. An optimal texture is in this case achieved by the process-related setting of the orientation of the grains in the electrical steel strip by means of two-stage manufacture with intermediate heat treatment during cold rolling, so that the grains have an energetically favorable crystallographic direction for magnetic reversals in the plane of the metal sheet. Due to a dehardened structure in the second rolling step, the two-stage cold rolling process with intermediate thickness allows simplified and sometimes more precise manufacture of lower final thicknesses of the highly silicized electrical steel strip.

The individual steps of the process of the invention are described in detail below:

Corresponding non-oriented electrical steel strips as are provided in step (A) of the process of the invention are known per se to a person skilled in the art. The thickness of the non-oriented electrical steel strip provided in step (A) is preferably from 1 to 4 mm, particularly preferably from 1.5 to 2.4 mm.

In general, it is possible to use any non-oriented electrical steel strip known to a person skilled in the art. The non-oriented hot-rolled strip provided in step (A) preferably has the following composition (all figures in % by weight)

-   -   from 2.1 to 3.6 of Si,     -   from 0.3 to 1.2 of Al,     -   from 0.01 to 0.5 of Mn,     -   up to 0.05 of Cr,     -   up to 0.005 of Zr,     -   up to 0.04 of Ni,     -   up to 0.05 of Cu,     -   up to 0.005 of C,     -   up to 0.005 of at least one rare earth metal,     -   up to 0.005 of Co,     -   balance Fe and unavoidable impurities.

The steel analysis which is preferably used for the purposes of the invention contains Si in an amount of from 2.1 to 3.6% by weight, preferably from 2.7 to 3.4% by weight. In the non-oriented electrical steel strip of the invention, Si has the effect of increasing the specific electrical resistance and reducing the magnetic losses. The minimum amount of Si should be at least 2.1% by weight since otherwise the specific electrical resistance is too low and thus the magnetic loss is too high and an austenite-ferrite phase transformation is to be avoided. If more than 3.6% by weight of Si is used for performing the invention, the formability deteriorates and the magnetic flux density is reduced too greatly.

The steel analysis which is preferably used according to the invention contains Al in an amount of from 0.3 to 1.2% by weight, preferably from 0.3 to 0.75% by weight. In the non-oriented electrical steel strip of the invention, Al has the effect of likewise increasing the specific electrical resistance. The minimum amount of Al should be at least 0.3% by weight, since otherwise the specific electrical resistance is too low and the magnetic loss is thus too high. If more than 1.2% by weight of Al is used in performing the invention, the cold formability deteriorates, in a particular case in combination with Si contents above 2.9% by weight.

The steel analysis which is preferably used according to the invention contains Mn in an amount of from 0.01 to 0.5% by weight, preferably from 0.07 to 0.3% by weight. In the non-oriented electrical steel strip of the invention, Mn has the effect of increasing the specific electrical resistance. The minimum amount of Mn should be at least 0.01% by weight, since otherwise the specific electrical resistance is too low and the magnetic loss is thus too high. If more than 0.5% by weight of Mn is used for performing the invention, the magnetic flux density decreases.

As additional alloy constituents, the hot-rolled, non-oriented electrical steel strip used in step (A) of the process of the invention can contain an element selected from the group consisting of up to 0.05% by weight of Cr, up to 0.005% by weight of Zr, up to 0.04% by weight of Ni, up to 0.05% by weight of Cu, up to 0.005% by weight of Ca, up to 0.005% by weight of at least one rare earth metal, up to 0.005% by weight of Co and mixtures thereof.

For the purposes of the present invention, unavoidable impurities are P, Ti, C, S, B and/or N.

If P is present, it tends to result in segregations which can be evened out only with difficulty and impairs the cold formability, the weldability and the oxidation resistance. If present, P is present in an amount of from 0.005 to 0.03% by weight.

If Ti is present, it increases the strength, in particular by formation of Ti carbides, and the corrosion resistance. Titanium precipitates influence the recrystallization of the grains in the slab. If present, Ti is present in an amount of from 0.001 to 0.006% by weight.

The presence of C is to be avoided where possible. C can be bound by carbide formers, for example Ti, Nb, Mo, Zr, W or Ta, and forms too large an amount of undesirable carbides (Al, Ti, Cr). If present, C is present in an amount of up to 0.005% by weight. If C is present in larger amounts, the magnetic aging which is then present increases the magnetic losses to an unacceptable extent.

If S is present, it forms sulfides, for example MnS, CuS and/or (Cu,Mn)S, which are bad for the magnetic properties of the material. If present, S is present in an amount of up to 0.005% by weight.

According to the invention, preference is given to the content of N being very low in order to reduce the formation of disadvantageous Al nitrides and/or Ti nitrides. Al nitrides can impair the magnetic properties. If present, N is present in an amount of not more than 0.005% by weight.

According to the invention, C, S, Ti and N are preferably present in the material of the invention in a total amount of not more than 0.01% by weight.

The provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip in step (A) of the process of the invention is preferably carried out by means of the conventional manufacturing route via a continuous casting plant or by thin slab manufacture. Both processes are known to a person skilled in the art.

The hot-rolled, optionally separately heat-treated, electrical steel strip from step (A) can preferably be used directly in step (B) of the process of the invention. In a further preferred embodiment of the process of the invention, the present invention relates to the process according to the invention in which a bell heat treatment is carried out at a temperature of from 640 to 900° C., preferably at a temperature of from 650 to 800° C., after step (A), i.e. before step (B).

Step (B) of the process of the invention comprises cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip.

In step (B) of the process of the invention, the hot-rolled electrical steel strip obtained from step (A) is cold rolled to a thickness of from 0.5 to 0.8 mm, preferably from 0.6 to 0.75 mm. Step (B) of the process of the invention is preferably carried out at a temperature of 240° C.

In a preferred embodiment of the process of the invention, the cold rolling in step (B) is carried out with a degree of cold rolling of from 30 to 90%, particularly preferably from 60 to 80%.

Step (B) of the process of the invention results in a first cold-rolled strip. This is preferably transferred directly to step (C) of the process of the invention.

Step (C) of the process of the invention comprises intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip.

Step (C) of the process of the invention is preferably carried out at a temperature of from 900 to 1050° C. According to the invention, step (C) can be carried out in any apparatus known to a person skilled in the art. Step (C) of the process of the invention is particularly preferably carried out in a continuous furnace.

Step (D) of the process of the invention comprises cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip.

In step (D) of the process of the invention, the intermediate-heat-treated, first cold-rolled strip obtained from step (C) is cold rolled in one or more steps to a thickness of from 0.24 to 0.36 mm. Step (D) of the process of the invention is preferably carried out at a temperature of up to 240° C.

In a preferred embodiment of the process of the invention, the cold rolling in step (D) is carried out with a degree of cold rolling of from 30 to 90%, particularly preferably from 40 to 80%.

Step (D) of the process of the invention results in a second cold-rolled strip. The formulations “first cold-rolled strip” and “second cold-rolled strip” are employed according to the invention to distinguish the cold-rolled strips from step (B) and from step (D). The second cold-rolled strip obtained in step (D) is preferably transferred directly to step (E) of the process of the invention.

Step (E) of the process of the invention comprises the final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip.

Step (E) of the process of the invention is preferably carried out at a temperature of from 950 to 1050° C. According to the invention, step (E) can be carried out in any apparatus known to a person skilled in the art. Step (C) of the process of the invention is particularly preferably carried out in a continuous furnace. After step (E) of the process of the invention, the non-oriented electrical steel strip of the invention having the above-described advantageous properties is obtained. Step (E) of the process of the invention can be followed by process steps known to a person skilled in the art, for example cutting, cleaning, reeling-up, etc.

All heat treatments in the process of the invention are preferably carried out at above 500° C. in an atmosphere which does not oxidize iron.

Magnetic properties which cannot be obtained in the combination of the features losses and polarization by means of single-stage cold rolling can be obtained by means of the process of the invention, in particular by the two-stage cold rolling with intermediate heat treatment.

The intermediate heat treatment dehardens the structure, as a result of which the force or energy required for the subsequent cold rolling steps to obtain the resulting intermediate thickness for the second cold rolling step is decreased and a lower final thickness can thus also be manufactured more precisely.

The present invention therefore also provides the non-oriented electrical steel strip produced by the process of the invention. A non-oriented electrical steel strip which can be made in a low thickness and displays particularly high polarization values J2500 and J5000 in combination with low magnetic losses both at low frequencies of, for example, 50 Hz and at high frequencies of, for example, 400 or 700 Hz can be provided by the production process of the invention, in particular by means of the steps (B), (C) and (D).

The present invention also provides the non-oriented electrical steel strip which has the following composition and texture (all figures in % by weight)

-   -   from 2.1 to 3.6 of Si,     -   from 0.3 to 1.2 of Al,     -   from 0.01 to 0.5 of Mn,     -   up to 0.05 of Cr,     -   up to 0.005 of Zr,     -   up to 0.04 of Ni,     -   up to 0.05 of Cu,     -   up to 0.005 of Cu,     -   up to 0.005 of at least one rare earth metal,     -   up to 0.005 of Co,     -   balance Fe and unavoidable impurities,         with

I _(ϵ,{554}<225>) −I _(ζ,{110}<001>)≤3,

where

-   -   I_(ϵ,{554}<225>) and I_(ζ,{110}<001>) have the following         meanings:     -   I_(ϵ,{554}<225>) intensity I in the ϵ-fiber of the orientation         density f(g) in Euler space at ϕ₁=90°, φ₂=45° and ϕ=60° and         orientation {554}<225> and     -   I_(ζ,{)110}<001> intensity I of the orientation density f(g) in         Euler space in the ζ-fiber at φ₁=0°, φ₂=0° and ϕ=45° and         orientation {110}<001>.

The intermediate heat treatment according to the invention (step (C)) influences the recrystallization and thus changes the texture. It can be shown by means of the examples according to the invention and the comparative examples that a less sharply pronounced texture is formed after the final heat treatment than in the case of a single-stage cold rolling after the final heat treatment.

In order to achieve low losses at high frequencies and high inductions or permeabilities, the microstructure is, according to the invention, set by means of two-stage cold rolling with an intermediate heat treatment so that an optimized texture is obtained.

For good magnetic properties, the intensity of the texture in the crystallographic direction or fiber α (<110>∥WR), η (<001>∥WR), ζ (<110>μNR) or θ (<001>∥WR), which comprises a forming magnetization direction having low magnetic losses, should be increased and the magnetically unfavorable γ-fiber ({111}∥BN) should be reduced. This can be shown, for example, by the orientation distribution function (OVF) and the orientation density (ODF) along the fibers.

The differences in the strength of the texture due to the process procedures with and without intermediate thickness can be established by determining orientation distribution functions (OVF). For this purpose, five samples per example are measured by means of X-ray diffraction (XRD). 30 μm are removed beforehand from each side of the sample by chemical surface treatment in order to rule out surface effects. The {110}, {200} and {211} pole figures are subsequently determined for each of the five samples using Co-Kα and the average of these measurements is calculated. The OVF is then determined from these average pole figures by means of a program. In order to be able to compare the OVFs more readily, sections of the orientation densities f(g) of the fibers (α, γ, ζ, ϵ) can be depicted and the intensities I in particular orientations compared.

The texture difference caused by the process procedures with and without intermediate thickness can be established via the difference between the intensities of the orientation densities f(g) of the ζ-fiber, which has a positive effect on the magnetic properties, with the orientation {110}<001>, and the magnetically unfavorable γ-skeletal line in the ϵ-fiber with the orientation {554}<225>, corresponding to I_(ϵ,{554}<225>)−I_(ζ,{110}<001>), which according to the invention is ≤3.

The present invention preferably provides the non-oriented electrical steel strip according to the invention which has a final thickness of from 0.24 to 0.36 mm. For the purposes of the present invention, “final thickness” means the thickness of the non-oriented electrical steel strip after the second cold rolling step.

Furthermore, the present invention preferably provides the non-oriented electrical steel strip according to the invention, where the polarization J2500/50 at 2500 A/m and 50 Hz and the magnetic loss P_(1.5/50) at 1.5 T and 50 Hz satisfy the following relationships:

-   -   in the case of hot-rolled strip material which has not been bell         heat treated: J_(2500/50)>−0.045*P_(15/50) ²+0.3*P_(15/50)+1.085         (1)     -   in the case of hot-rolled strip material which has been bell         heat treated: J_(2500/50>)−0.045*P_(15/50)         ²+0.28*P_(15/50)+1.165 (2).

The magnetic losses P can, according to the invention, be determined by all methods known to a person skilled in the art, in particular by means of an Epstein frame, in particular in accordance with DIN EN 60404-2:2009-01: Magnetic materials—Part 2: Methods of measurement of the magnetic properties of electrical steel strip and sheet by means of an Epstein frame”. Here, appropriate electrical steel sheets are cut into longitudinal and transverse strips and measured as mixed sample in the Epstein frame.

The non-oriented electrical steel strip described here characterizes an anisotropy of the magnetic loss values at 1.5 T and 50 Hz in the longitudinal and transverse direction of less than 20%.

The present invention also provides for the use of a non-oriented electrical steel strip according to the invention in iron cores of rotating electric machines, in particular in electric motors and generators.

FIGURES

FIG. 1 shows the improvement according to the invention in the case of hot-rolled strip material which has not been bell heat treated from examples 1, 2, 5 and 6.

FIG. 2 shows the improvement according to the invention in the case of hot-rolled strip material which has been bell heat treated from examples 3, 4, 7, 8, 13, 14 and 15 to 18.

FIG. 3 shows the orientation densities of the ODF along the ϵ-fibers in Euler space at φ₁ at 90°, φ₂ at 45° and ϕ in the range from 0° to 90° for example 1.

FIG. 4 shows orientation densities of the ODFs along the ζ-fibers in Euler space at ζ₁=0° to 90°, φ₂ at 0° and ϕ at 45° for example 1.

FIG. 5 shows orientation densities of the ODF along the ϵ-fibers in Euler space at φ₁=90°, ϕ₂=45° and ϕ in the range from 0° to 90° for example 2.

FIG. 6 shows orientation densities of the ODFs along the ζ-fibers in Euler space at φ₁ of from 0° to 90°, φ₂ at 0° and ϕ at 45° for example 2.

EXAMPLES

The following working examples serve to illustrate the invention. The compositions 1, 2 and 3 as per table 1 are used.

TABLE 1 No. Si Al Mn C Cr Ni N S Ti P Nb Mo 1 3.14 0.656 0.15 0.0023 0.028 0.013 0.002 0.006 0.001 0.009 0.002 0.15 2 3.17 0.639 0.163 0.0017 0.028 0.013 0.0017 0.0005 0.0045 0.012 0.001 0.0011 3 3.133 0.623 0.151 0.0031 0.033 0.012 0.0012 0.0005 0.0027 0.010 0.001 0.0012 All figures in % by weight, balance Fe

Example 1

Composition 1 as per table 1 is used in example 1.

Examples 5, 6, 7 and 8 according to the invention and comparative samples 1, 2, 3 and 4 were produced. For this purpose, the slab obtained after melting of a composition 1 from table 1 was in each case hot rolled, optionally subjected to a hot-rolled strip bell heat treatment at 740° C. and cold rolled to an intermediate thickness of 0.70 mm. The material was subsequently subjected to intermediate heat treatment at 1000° C., cold rolled to a final thickness of 0.34 mm and then subjected to final heat treatment in the range from 1000° C. to 1080° C. The comparative sample 4 was hot rolled after melting, subjected to hot-rolled strip heat treatment, directly cold rolled to a final thickness of 0.34 mm and subjected to final heat treatment at 1000° C. Comparative example 3 results from the standard process, i.e. single-stage cold rolling with hot-rolled strip bell heat treatment. For details, see table 2.

The characteristic magnetic values, i.e. J100, J5000, J2500, P1.5/50 and P1.0/400, were in each case determined for samples with and without intermediate thickness after final heat treatment. The values for the polarization J of the examples according to the invention over the field strength range up to saturation at both tested frequencies 50 Hz and 400 Hz are higher than the values of the comparable comparative examples with the same thickness of 0.35 mm.

TABLE 2 Experiments according to the invention and comparative experiments as per example 1 HG Intermediate ZG Final SG Temperature thickness Temperature thickness Temperature J100 μ_(r) at J5000 J2500 P1.5/50 P1.0/400 No. [° C.] [mm] [° C.] [mm] [° C.] [T] 0.8 T μ_(max) [T] [T] [W/kg] [W/kg] 1 Comparison — — — 0.34 1080 0.994 8747 8748 1.602 1.509 2.362 17.498 2 Comparison — — — 0.34 1000 0.819 6529 6529 1.598 1.508 2.781 18.043 3 Comparison 740 — — 0.34 1100 1.053 9816 9816 1.643 1.549 2.141 16.432 4 Comparison 740 — — 0.34 1000 0.823 6553 6553 1.642 1.551 2.694 18.127 5 According — 0.7 1000 0.34 1080 0.952 8108 8164 1.654 1.559 2.201 16.736 to the invention 6 According — 0.7 1000 0.34 1050 1.085 9546 9546 1.667 1.578 2.120 15.782 to the invention 7 According 740 0.7 1000 0.34 1080 1.103 10094 10094 1.675 1.584 2.027 15.750 to the invention 8 According 740 0.7 1000 0.34 1050 1.072 9828 9828 1.670 1.577 2.077 16.223 to the invention HG optional bell heat treatment of the hot-rolled strip ZG intermediate heat treatment SG final heat treatment — not carried out

Example 2

Examples 11, 12 and 13 according to the invention having the composition 2 as per table 1, example 14 having the composition 3 and comparative examples 9 and 10 having the composition 2 of table 1 were produced under the conditions shown in table 3.

TABLE 3 HG Intermediate ZG Final SG Temperature thickness Temperature thickness Temperature J2500 J5000 P1.5/50 P1.0/400 Example [° C.] [mm] [° C.] [mm] [° C.] [T] [T] [W/kg] [W/kg]  9 Comparison 740 — — 0.29 1060 1.543 1.639 2.23 15.09 10 Comparison 740 — — 0.29 1030 1.542 1.637 2.28 14.94 11 According to 740 0.64 980 0.29 1030 1.578 1.672 2.06 14.02 the invention 12 According to 740 0.64 980 0.29 1000 1.573 1.666 2.19 14.46 the invention 13 According to 740 0.64 980 0.29 1050 1.573 1.666 2.10 14.47 the invention 14 According to 740 0.64 980 0.29 1030 1.572 1.664 2.18 14.68 the invention HG optional bell heat treatment of the hot-rolled strip ZG intermediate heat treatment SG final heat treatment — not carried out

The improvement achieved both in the magnetization losses and also the magnetic polarization in the case of manufacture according to the invention can be described by the relationships shown in formula 1 and formula 2 and are depicted in FIGS. 1 (for hot-rolled strip which has not been bell heat treated) and 2 (for hot-rolled strip which has been bell heat treated).

Formula 1 (for hot-rolled strip material which has not been bell heat treated): J_(2500/50)>−0.045*P_(15/50) ²+0.3*P_(15/50)+1.085

Formula 2 (for hot-rolled strip material which has been bell heat treated): J_(2500/50)>−0.045*P_(15/50) ²+0.28*P_(15/50)+1.165

X-ray texture determinations using CoKα radiation were carried out and the {100}, {200} and {211} pole figures of the finally heat treated samples 1, 3, 5, 7, 9, 11, 12 and 14 were determined. To obtain better measurement statistics, 5 X-ray samples were measured for each of the samples. The orientation distribution functions (OVF) were calculated from the average pole figures.

The orientation of the crystal coordinate system relative to the sample coordinate system can be depicted by the OVF by each point in a space spanned by the Euler angles φ₁, φ₂ and ϕ being assigned an orientation density f(g) or intensity I. For a pictorial representation, these orientation distribution functions can be depicted with the aid of the intensity of fibers in sectional areas of this space.

Here, the ϵ-fiber and the ζ-fiber are examined. In the ϵ-fiber, the <110> direction lies parallel to the transverse direction and runs at φ₁=90°, φ₂=45° and ϕ in the range from 0° to 90°. In the case of the ζ-fiber, the <110> direction lies parallel to the normal direction and runs at φ2=0°, ϕ=45° and φ1=0° to 90°.

For the section of the OVF relevant for the respective fiber, the orientation densities f(g) of the ζ-fiber and ϵ-fiber were plotted for the course of Euler angles of from 0 to 90°.

FIGS. 3 to 6 show the course of the OVF versus the angle ϕ for the ϵ-fiber and the angle φ₁ for the ζ-fiber. The specific positions {554}<225>, {110}<001> and more are drawn in.

The samples 1, 3 and 9 of the single-stage manufacture have the main intensity of their texture in the vicinity of the magnetically poor γ-fiber or the γ-skeletal line (see {554}<225> in the ϵ-fiber).

Here, the ϵ-fiber at {554}<225> contributes to a worsened texture since the ideal γ-fiber can be shifted by the manufacture by some degrees, which is referred to as γ-skeletal line. A skeletal line refers to a connecting line of points of greatest intensity through Euler space and intensity fluctuations along this can be interpreted as fluctuations within the manufacturing tolerance. For this reason, the maximum intensity I of the γ-fiber shifts to the ϵ-fiber at φ₁ at 90°, φ₂ at 45° and ϕ at 60° and orientation {554}<225>. The process according to the invention of two-stage manufacture reduces the orientation density of this disadvantageous ϵ-fiber texture value at {554}<225> (see table 3 and FIGS. 3 to 6 ).

The ζ-fiber, which does not contain any magnetically difficult magnetization reversal direction, is occupied more strongly in the case of the two-stage manufacture according to the invention than in the case of the single-stage manufacture. The individual values are shown in table 4.

TABLE 4 Texture I_(ε,{554}<225>) − I_(ε,{554}<225>) − sample Example I_(ε,{554}<225>) I_(ζ,{110}<001>) I_(ζ,{110}<001>) I_(ζ,{110}<001>) ≤ 3 1  1 Comparison 6.8 0 6.8 No 3  3 Comparison 8.0 1.1 6.9 No 2  5 According to 1.5 1.8 −0.3 Yes the invention 4  7 According to 0.4 5.0 −4.6 Yes the invention 4  9 Comparison 7 0 7 No 1 11 According to 3.5 2.2 1.3 Yes the invention 2 12 According to 2 4.2 −2.2 Yes the invention 3 14 According to 2.9 2.5 0.4 Yes the invention I_(ε,{554}<225>) Intensity I of the orientation density f(g) in Euler space in the ε-fiber at φ₁ = 90°, φ₂ = 45° and ϕ = 60° and orientation {554}<225> I_(ζ,{110}<001>) Intensity I of the orientation density f(g) in Euler space in the ζ-fiber at φ₁ = 0°, φ₂ = 0° and ϕ = 45° and orientation {110}<001>

An improvement in the texture is achieved by the two-stage manufacture since the two-stage manufacture brings about the increase in the intensity of the orientation density at {110}<001> in the ζ-fiber and the lowering of the intensity of the orientation density at {554}<225>in the ϵ-fiber (see table 4). Non-oriented electrical steel strip which has been produced by manufacture according to the invention with intermediate thickness and which satisfies the condition

I _(ϵ,{554}<225>) −I _(ζ,{110}<001>)<3

therefore has particularly good magnetic properties.

INDUSTRIAL APPLICABILITY

The process of the invention makes it possible to produce a non-oriented electrical steel strip which displays particularly low magnetic losses both at low frequencies and at high frequencies and displays good rollability so that it can be rolled particularly thin. It can therefore be used advantageously in rotating electric machines, in particular in electric motors and generators. 

1. A non-oriented electrical steel strip comprising the following composition and texture (all figures in % by weight) from 2.1 to 3.6 of Si, from 0.3 to 1.2 of Al, from 0.01 to 0.5 of Mn, up to 0.05 of Cr, up to 0.005 of Zr, up to 0.04 of Ni, up to 0.05 of Cu, up to 0.005 of Cu, up to 0.005 of at least one rare earth metal, up to 0.005 of Co, balance Fe and unavoidable impurities, with I _(ϵ,{554}<225>) −I _(ζ,{110}<001>)<3, where I_(ϵ,{554}<225>) and I_(ζ,{110}<001>) have the following meanings: I_(ϵ,{554}<225>) intensity I in the ϵ-fiber of the orientation density f(g) in Euler space at φ₁=90°, φ₂=45° and ϕ=60° and orientation {554}<225> and I_(ζ,{110}<001>) intensity I of the orientation density f(g) in Euler space in the ζ-fiber at φ₁=0°, φ₂=0° and ϕ=45° and orientation {110}<001>.
 2. The non-oriented electrical steel strip as claimed in claim 1, wherein the non-oriented electrical steel strip has a final thickness of from 0.24 to 0.36 mm.
 3. The non-oriented electrical steel strip as claimed in claim 2, wherein the polarization J_(2500/50) at 2500 A/m and 50 Hz and the magnetic loss P_(1.5/50) at 1.5 T and 50 Hz satisfy the following relationships after the final heat treatment: for hot-rolled strip material which has not been bell heat treated: J_(2500/50)>−0.045*P_(15/50) ²+0.3*P_(15/50)+1.085 (1) for hot-rolled strip material which has been bell heat treated: J_(2500/50)>−0.045*P_(15/50) ²+0.28*P_(15/50)+1.165 (2).
 4. A process for producing a non-oriented electrical steel strip as claimed in claim 3 , comprising at least the following process steps: (A) provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip, by a conventional manufacturing route via a continuous casting plant or by thin slab manufacture, in a thickness of from 1 to 4 mm, (B) cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip, (C) intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip, (D) cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip; and (E) final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip.
 5. The process as claimed in claim 4, wherein step (C) is carried out in one of a continuous furnace and as bell heat treatment.
 6. The process as claimed in claim 5, wherein the cold rolling in step (B) is carried out with a degree of cold rolling of from 30 to 90%.
 7. The process as claimed in claim 6, wherein the cold rolling in step (D) is carried out with a degree of cold rolling of from 30 to 90%.
 8. The process as claimed in claim 7, wherein a hot-rolled strip bell heat treatment is carried out at a maximum temperature of from 640 to 900° C. in step (A).
 9. A non-oriented electrical steel strip produced by the process as claimed in claim
 8. 10. An electric motor comprising: an iron core having the non-oriented electrical steel strip as claimed in claim
 3. 